Improving the estimation of thermospheric neutral density via two-step assimilation of in situ neutral density into a numerical model

Earth, Planets and Space

Table 1 The quantities that are perturbed to generate the ensemble are listed in the first column

	Units	Standard deviation	Truncation	Min	Max
External forcing
F10.7	sfu	1	± 50	75.9	87.8
Hemispheric power	GW	5	± 9	15.3	155.0
Cross tail potential	kV	8	± 12	23.2	170.4
Solar wind density	\(\text {1/cm}^{3}\)	0.1	± 0.3	0.5	27.1
Solar wind velocity	km/h	45	± 135	329.3	820.8
Lower boundary conditions
Neutral temperature	K	3	± 9	151.5	198.8
Neutral zonal wind	cm/s	500	± 1500	− 5914.5	5841.5
Neutral meridional wind	cm/s	650	± 1950	− 8073.3	8077.5
Geopotential height	m	70	± 210	97246.7	98652.7
Constants
Characteristic Maxwellian energy of polar cusp electrons	keV	0.01	± 0.03	0.1
Characteristic Maxwellian energy of drizzle electrons	keV	0.05	± 0.15	0.5
Joule heating factor	–	0.15	± 0.45	1.5

The solar wind parameters are only perturbed if the Weimer model is used. Whereas hemispheric power and cross tail potential are only perturbed in case of the Heelis model. The third and fourth column are the parameters used for sampling the truncated normal distributions. The mean is always zero. Note that correlations are not listed in this table. The truncation is symmetric. That means values larger than the positive truncation threshold as well as values less than the negative truncation threshold are rejected. The last two columns contain the minimal and maximal values of the unperturbed quantities during the experiment